Realmente no entiendo por qué await
y async
no mejoran el rendimiento de mi código aquí like they're supposed to.¿Por qué el async CTP funciona mal?
Aunque escéptico, pensé que se suponía que el compilador reescribiera mi método para que las descargas se hicieran en paralelo ... pero parece que en realidad no está sucediendo.
(me hago dan cuenta de que await
y async
no crean hilos separados;? Sin embargo, el sistema operativo debe estar haciendo las descargas en parallal, y volver a llamar mi código en el hilo original - ¿no debería)
¿Estoy usando async
y await
incorrectamente? ¿Cuál es la forma correcta de usarlos?
Código:
using System;
using System.Net;
using System.Threading;
using System.Threading.Tasks;
static class Program
{
static int SumPageSizesSync(string[] uris)
{
int total = 0;
var wc = new WebClient();
foreach (var uri in uris)
{
total += wc.DownloadData(uri).Length;
Console.WriteLine("Received synchronized data...");
}
return total;
}
static async Task<int> SumPageSizesAsync(string[] uris)
{
int total = 0;
var wc = new WebClient();
foreach (var uri in uris)
{
var data = await wc.DownloadDataTaskAsync(uri);
Console.WriteLine("Received async'd CTP data...");
total += data.Length;
}
return total;
}
static int SumPageSizesManual(string[] uris)
{
int total = 0;
int remaining = 0;
foreach (var uri in uris)
{
Interlocked.Increment(ref remaining);
var wc = new WebClient();
wc.DownloadDataCompleted += (s, e) =>
{
Console.WriteLine("Received manually async data...");
Interlocked.Add(ref total, e.Result.Length);
Interlocked.Decrement(ref remaining);
};
wc.DownloadDataAsync(new Uri(uri));
}
while (remaining > 0) { Thread.Sleep(25); }
return total;
}
static void Main(string[] args)
{
var uris = new string[]
{
// Just found a slow site, to demonstrate the problem :)
"http://www.europeanchamber.com.cn/view/home",
"http://www.europeanchamber.com.cn/view/home",
"http://www.europeanchamber.com.cn/view/home",
"http://www.europeanchamber.com.cn/view/home",
"http://www.europeanchamber.com.cn/view/home",
};
{
var start = Environment.TickCount;
SumPageSizesSync(uris);
Console.WriteLine("Synchronous: {0} milliseconds", Environment.TickCount - start);
}
{
var start = Environment.TickCount;
SumPageSizesManual(uris);
Console.WriteLine("Manual: {0} milliseconds", Environment.TickCount - start);
}
{
var start = Environment.TickCount;
SumPageSizesAsync(uris).Wait();
Console.WriteLine("Async CTP: {0} milliseconds", Environment.TickCount - start);
}
}
}
Salida:
Received synchronized data...
Received synchronized data...
Received synchronized data...
Received synchronized data...
Received synchronized data...
Synchronous: 14336 milliseconds
Received manually async data...
Received manually async data...
Received manually async data...
Received manually async data...
Received manually async data...
Manual: 8627 milliseconds // Almost twice as fast...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Received async'd CTP data...
Async CTP: 13073 milliseconds // Why so slow??
Oh, eh, esto se ve mucho más limpio. =) Gracias! – Mehrdad